<!DOCTYPE html>
<html>
<head>
	<meta charset="utf-8">
	<title>canvas</title>
</head>
<body>

	<canvas id="canvas" width="200" height="100" style="border: 1px solid #ccc;">
		当前浏览器不支持HTML5 canvas标签
	</canvas>

	<script type="text/javascript">
		

		window.onload = function() {

			var c=document.getElementById("canvas");

			var ctx=c.getContext("2d");

			ctx.beginPath();

			ctx.arc(100,50,40,0,2*Math.PI);

			ctx.stroke();

		}

	</script>

</body>
</html>